1. Field of the Invention
The present invention relates to a thermosetting resin composition for steel inserts, and more particularly, to a thermosetting resin composition for steel inserts which is lightweight and has excellent physical properties, particularly through use of a glass fiber and a thermosetting resin composite containing an unsaturated polyester resin.
2. Discussion of Related Art
In connection with efforts to provide energy savings and reduce impact on the environment, steady research has been conducted towards replacing heavy steel materials with a lightweight plastic material. Such lightweight plastic materials could potentially improve fuel efficiency and increase the power output, etc. of vehicles.
One essential goal is to manufacture a lightweight electric automobile. However, electric automobiles exhibit poor power output and fuel efficiency compared with automobiles equipped with an internal combustion engine. Thus, leading global automobile companies have devoted significant time towards manufacturing a lightweight car body using plastic materials.
Among the plastic materials currently used to manufacture a lightweight automobile thermosetting resin is the most widely used. A thermosetting resin is a resin whose shape is not changed even when the resin is molded by application of heat and pressure using a curing reaction, followed by applying heat again to the molded product.
Thermosetting resins typically have excellent heat resistance, chemical resistance, mechanical properties and electrical insulating properties. Further, such thermosetting resins may be prepared into a molded product having excellent physical properties since the thermosetting resin includes a filler. In particular, the thermosetting resin may be prepared into a fiber-reinforced plastic since a reinforced fiber, such as a glass fiber, is added to the thermosetting resin.
Although the filler and the reinforced fiber are added to the thermosetting resin to prepare a thermosetting resin composition having relatively excellent physical properties, the thermosetting resin has a problem in that it is not applicable to structures which must continuously withstand high loads.
In an attempt to solve this problem, a method has been developed by which a steel-reinforced material is locally used to make up for insufficient physical properties of the thermosetting resin. However, is problematic to use the steel-reinforced material locally in large panel parts, such as a lower battery case for electric vehicles. Therefore, a method has been developed in which a steel-reinforced material is added to a thermosetting resin composition and the thermosetting resin composition is molded into the large panel shape.
FIG. 1 is a three-dimensional diagram of a steel sheet 100 that is inserted into a lower case of a battery, and FIG. 2 is a three-dimensional diagram of a lower case of a battery for electric vehicles into which the steel sheet 100 is inserted. When a reinforced material of a steel sheet 100 shown in FIGS. 1 and 2 is first inserted into the thermosetting resin composition and the thermosetting resin composition is then molded, especially when the thermosetting resin composition is put into a mold, the flow of the thermosetting resin composition injected into the mold is hampered due to the presence of the steel sheet 100 distributed over the thermosetting resin composition. This results in inferior goods such as a poorly molded product.
Also, since there is a difference in shrinkage rate between the thermosetting resin composition and the steel sheet during a cooling process, even after the molding is completed, the interface between the thermosetting resin composition and the steel sheet may become separated.